Alkylphenol sulfides are conventionally known as an antioxidant (e.g., U.S. Pat. Nos. 2,239,534, 3,377,334), a rubber sulfurizer (e.g., U.S. Pat. Nos. 3,468,961, 3,647,885), a polymer stabilizer (e.g., U.S. Pat. Nos. 3,882,082, 3,845,013, 3,843,600), an anticorrosive (e.g., U.S. Pat. No. 3,684,587), and a starting material for phenates for use as a lubricating-oil additive (Hori et al., Sekiyu Gakkai-shi, Vol. 34, p. 446, 1991).
Known processes for producing conventional phenol sulfides include a method in which a phenol and elemental sulfur are used as starting materials (e.g., A. J. Neale et al., Tetrahedron, Vol. 25, p. 4593, 1969); a method in which a phenol, elemental sulfur, and a base catalyst are used as starting materials (e.g., U.S. Pat. No. 3,468,961); a method in which a phenol, elemental sulfur, and a molecular halogen are used as starting materials (e.g., B. Hortling et al., Polym. Bull., Vol. 8 (1982), p.1); a method in which a phenol reacts with an aryl disulfide in the presence of a base catalyst (e.g., T. Fujisawa et al., J. Org. Chem., Vol. 33 (1973), p.687); a method in which a phenol and a sulfur halide are used as starting materials (e.g., U.S. Pat. No. 2,239,534); and a method in which a halogenated phenol reacts with a sulfurized alkali metal reagent.
However, they disclose an oligomer containing 2,2'-thiobis(4-alkylphenol) (dimer), 2-[3-(2-hydroxy-5-alkylphenylthio)-2-hydroxy-5-alkylphenylthio]-4-alkylphe nol (trimer), or 2-[3-[3-(2-hydroxy-5-alkylphenylthio)-2-hydroxy-5-alkylphenylthio]-2-hydro xy-5-alkylphenylthio]-4-alkylphenol (tetramer), or a composition containing such an oligomer, and a process for the production thereof. Namely, the alkylphenol sulfides dealt with in those references are all non-cyclic compounds, and the existence of a cyclic phenol sulfide and a method for producing the same have not been disclosed.